Experimental study on strength characteristics and constitutive behavior of frozen chloride silty clay

Artificial ground freezing (AGF) technology is sometimes adopted to reinforce the surrounding soil to ensure the safety of subway tunnels during construction in the eastern coastal areas of China. The mechanical characteristics of frozen soil are subjected to change due to the incorporation of chlorine salt, and the soil strength decreases significantly with an increase of salt content. The mechanical properties of frozen silty clay have been rarely investigated due to the coupling effect of temperature, strain rate, and salt content. In this study, before the application of AGF, a series of unconfined compressive strength (UCS) tests and the consolidated-undrained static triaxial compression tests were conducted on frozen silty clay to investigate the influence of salt content, temperature, and strain rate on the mechanical properties of frozen soil. From the stress-strain curves of the UCS test, strain-hardening and strain-softening behavior were identified as a result of the influence of different temperatures and salt contents. Regression analysis was performed to discriminate the effect of each individual factor and their coupling effect. The results reveal that soil UCS logarithmically increased with a decrease in relative temperature and strain rate. Both UCS and static triaxial strength linearly decreased with an increase in salt content. The influence of salt content on the strength of frozen soil was discussed and compared with previous researches. Furthermore, an elastic-plastic constitutive model was proposed to characterize the stress-strain behavior in which the effects of strain rate and salt content were included. At last, with consideration of salt content, a modified constitutive model was proposed to describe the strength and deformation behavior of frozen silty clay.